1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine tool, and particularly to a numerical controller capable of performing a multi-system control.
2. Description of Related Art
There has been carried out that an industrial machine such as a machine tool is controlled by a numerical controller with a plurality of control systems independently from or synchronously with one another. In such control, there is a case where each control system has a spindle and a case where one spindle is controlled alternately by different control systems.
For example, in a case where a workpiece is attached to spindles respectively controlled to rotate in synchronism by different control systems, there possibly occurs a time delay in starting the spindles controlled by the respective control systems to cause a damage on the workpiece. So as to prevent this, there is proposed a numerical controller in which a machining program for one control system includes a spindle control command for the other control system, and command data for controlling the spindles are issued simultaneously to the one control system and the other control system based on the machining program for the one control system to eliminate the time delay in starting the spindles so as to operate the spindles simultaneously (see JP 3-71205A).
In the conventional numerical controller having a plurality of control systems, when control of a spindle by one control system is to be transferred to another control system, the transfer of the spindle control has to be performed in a state where the spindle is stopped. There is no problem in transferring the control of the spindle when the spindle is stopped, but in a case where the spindle is in rotation by one control system, it is required that the rotation of the spindle is decelerated to stop and then the control of the spindle is transferred to the other control system. Thus, there arises a problem of taking a considerable time for transferring of the control of the spindle.